Antennas are important components of equipment that performs wireless communication. They are widely used in systems such as radio broadcasting, broadcast televisions, two-way radios, communications receivers, wireless computer networks, cell phones, and satellite communications, as well as other devices such as garage door openers, wireless microphones, Bluetooth-enabled devices, walkie-talkies, baby monitors, and RFID tags on merchandise. As communications technologies advance, antenna design is facing new challenges such as requirements of supporting multiband and multimode services, supporting additional frequency bands using wideband code division multiplexing access (WCDMA) and 3GPP Long Term Evolution (LTE), supporting more radio access technologies and thinner ID.
When a part of a human body, such as head or a hand, approaches or contacts an antenna of a hand-held communication device, such as a smart phone or a tablet, the antenna experiences reduced system efficiency, which degrades performance. The performance degradation is especially serious for antennas within a metal housing or chassis. The efficiency loss may be compensated by utilizing antenna tuning methods. Conventional antenna tuning methods monitor changes on an antenna's impedance, using phase or voltage standing wave ratio (VSWR), and seek to match the antenna's impedance to that of the antenna feed line. These methods rely on the transmitter to measure the VSWR or phase of a matched antenna to do closed loop control and the tuning may not be optimal when transmitting power is low.